The present invention relates to a developer used in an electrophotographic image forming apparatus such as a copier, a facsimile machine, a printer or the like, and also relates to a developer cartridge, a developing device and the image forming apparatus.
A general toner (developer) includes a colored resin particle and an external additive added to a surface of the colored resin particle. The external additive is formed of inorganic or organic substance, and is added in order to obtain a desired flowability and charging characteristics. The external additive contains, for example, a hydrophobic silica fine powder having a number-average primary particle diameter of 7-16 [nm], a colloidal silica fine powder having a number-average primary particle diameter of 65-100 [nm], and a nitrogen-containing resin particle having a number-average primary particle diameter of 200-300 [nm]. By using such a toner, a decrease in flowability of the toner during a continuous printing is suppressed, and deterioration of image quality is suppressed. See, for example, Japanese Patent Application Publication No. 2012-242492 (Page 32 and FIG. 1).
However, in the toner of the above described document, the nitrogen-containing resin particle may easily separate from the surface of the colored resin particle, and may cause ghost. When a large amount of the external additive is added to the toner in order to reduce a cohesion degree (i.e., to increase a flowability), the ghost is more likely to occur. Therefore, it is difficult to obtain a toner having a desired flowability (i.e., capable of suppressing image blurring) and capable of suppressing ghost.